The present invention relates to a cooling arrangement for a liquid-cooled internal-combustion engine of a motor vehicle. More particularly, the present invention is directed to a cooling arrangement comprising a radiator which is connected to the forward flow pipe and the return flow pipe of a coolant circuit of the internal-combustion engine and which either has its own closable feed opening or is fluidically connected with an expansion tank having a closable feed opening. A temperature-controlled thermostatic valve provides that the coolant is completely or partially either guided through the radiator or past the radiator by a short-circuit pipe between the forward flow pipe and the return forward pipe. The thermostatic valve is electrically heatable in order to limit or reduce the coolant temperature in the coolant circuit of the internal-combustion engine to a value which is lower in comparison to the unheated condition.
A cooling arrangement is described in German Patent Application P 43 24 178 which is not admitted prior art because it is not a prior publication. The temperature-controlled thermostatic valve of that arrangement controls the coolant temperature to an upper limit temperature during the warm-up operation and/or during the mixed operation without any heating of the expansion element of the thermostatic valve. A control unit releases, as a function of detected operating and/or environmental quantities of the internal-combustion engine as required, the heating of the expansion element. This shifts the method of operation of the cooling arrangement from the warm-up operation or from the mixed operation of the upper operating limit temperature to the mixed operation or cooling operation of a coolant temperature which is lower in comparison to the upper operating limit temperature. Because the expansion element of the thermostatic valve operates as a function of detected operating and/or environmental quantities of the internal-combustion engine, an electronic control unit is required in which the detected operating and/or environmental quantities of the internal-combustion engine are processed in a suitable manner and are used for controlling the heating of the expansion element.
The upper operating limit temperature is preferably identical to the operating temperature of the internal-combustion engine which is most advantageous with respect to the consumption and is slightly lower than the maximally permissible operating temperature of the internal-combustion engine. Preferably, the upper operating limit temperature will be above 100.degree. C., particularly at approximately 105.degree. C. The maximally permissible operating temperature is the highest possible temperature at which the internal-combustion engine can be normally operated without disturbances over an extended time period. As a result, even with failure of the electric heating of the expansion element, damage to the internal-combustion engine is prevented. The maximally permissible operating temperature is normally between 105.degree. C. and 120.degree. C.
If the expansion element is not heated electrically, an opening cross-section to the radiator occurs only as a function of the coolant temperature. This opening cross-section controls the coolant temperature to the defined upper operating limit temperature. For example, by the selection of a corresponding material with a temperature-dependent density and by a suitable construction, at a defined upper operating limit temperature, the opening cross-section of the radiator is still not maximal. That is, no pure radiator operation is achieved. Thus, by an additional heating of the expansion element, a further enlargement of the opening cross-section, and thus a displacement in the direction of the radiator operation, is possible.
European Patent EP 0 184 196 B1 describes a cooling arrangement which contains a bypass flow return pipe from the expansion tank provided with the feed opening, while bypassing the thermostatic valve, to the connection of the return flow pipe on the internal-combustion engine. For feeding coolant into the cooling system during the first feeding or during the refilling, the coolant is provided through the feed opening. While bypassing the thermostatic valve, the coolant is distributed by the bypass flow return pipe in the coolant circuit of the internal-combustion engine. By way of the return flow pipe, the coolant flows from the internal-combustion engine into the radiator. Because the pipe cross-sections are sized according to the operational requirements of the cooling system, the feeding operation is time-consuming. As a rule, the bypass flow return pipe has a smaller diameter than the forward flow pipe, and the return flow pipe and also the temperature-controlled thermostatic valve guide the cold coolant through the short circuit pipe and not through the radiator.
In order to ensure that no significant air will remain in the cooling system after a feeding, the internal-combustion engine will be idled for some time while the feed opening is open. In order to meet the consumption and emission requirements of the internal-combustion engine, the internal-combustion engine is run in the warm-up phase and in the partial-load operation at increased coolant temperatures to above the boiling temperature of the coolant. The opening temperature of the thermostatic valve corresponds to these coolant temperature data. If now, after the filling of the cooling system, the internal-combustion engine is operated while the cooling system is open, the temperature-controlled thermostatic valve will not respond, or only respond very little, when the boiling temperature of the coolant is reached. This occurs at ambient pressure. Thus, during the filling of the radiator during idling while the feed opening is open, a coolant temperature in the coolant circuit of the internal-combustion engine is above the boiling temperature. This is because the thermostatic valve, due to its high response temperature, guides the coolant essentially through the short-circuit pipe between the forward flow pipe and the return flow pipe and not through the radiator. While the expansion tank is open, coolant temperatures can occur in the cooling system at ambient pressure which are above the boiling temperature during the opening of the thermostatic valve. Then the hot coolant will be ejected, partially in the manner of a geyser, through the radiator forward flow pipe or the expansion tank forward flow pipe and the feed opening.
It is, therefore, an object of the present invention to ensure, that the ventilation is concluded before the boiling temperature is reached or that the thermostatic valve will open up before the boiling temperature is reached. Thus, the temperature will therefore not rise further. This occurs during the filling of the cooling system and the subsequent ventilation phase of the cooling system while the feed opening of the radiator or of the expansion tank is open.
This object has been achieved according to the present invention by comparing the distance covered by the motor vehicle after the vehicle start with a determined limit distance. Consequently, when the limit distance is covered in normal driving, the coolant temperature in the coolant circuit of the internal-combustion engine remains clearly below the opening temperature of the thermostatic valve containing no current and thus under the boiling temperature. From the vehicle start, however, the thermostatic valve will have a current assuming that the distance covered after the vehicle start is shorter than the limit distance.
During the warm-up phase of the internal-combustion engine, immediately after the filling of the radiator, the feed opening remains open for ventilating the cooling system. Because long distances are not covered during that phase, the thermostatic valve will permanently have current during the entire warm-up and ventilating operation. Due to the application of current, and therefore the electric heating of the thermostatic valve, the coolant temperature in the coolant circuit of the internal-combustion engine is limited to a value which is low in comparison to the unheated condition. Specifically, the value is below the boiling temperature of the coolant at ambient pressure. The opening of the thermostatic valve during the increasing heating of the coolant in the coolant circuit of the internal-combustion engine occurs at a temperature which is low in comparison to the boiling temperature of the coolant. As a result, the coolant, which now arrives in the radiator or in its expansion tank, because of the low temperature, is not ejected through the feed opening. Thus, a person carrying out the filling avoids being scalded.
Because the vehicle speed signal is already determined in the vehicle, the covered distance can advantageously be determined by integrating the vehicle speed signal.
According to another advantageous further embodiment of the present invention, the limit distance is determined as a function of the coolant temperature at the vehicle start. That is, the limit distance is determined to be longer when the the coolant temperature at the time of the vehicle start is lower.